1. Field of Invention
The present invention relates to a power amplifier. More particularly, the present invention relates to an audio power amplifier.
2. Description of Related Art
An audio system generally consists of three parts. The first part is an audio source, such as a tape player, a disc player or an RF tuner, for retrieving audio information and converting it into an electrical signal. The second part of the audio system is a loudspeaker. The loudspeaker converts electrical signals into acoustic waves to be perceived by a listener. The third part of the audio system is a power amplifier. The power amplifier amplifies the electrical signal from the audio source and supplies the necessary current to drive the loudspeaker.
Since the audio power amplifier is provided to amplify the audio signal from the audio source and supply the necessary current to drive the loudspeaker, it plays an important role in the audio system. However, when a power voltage, which is used for powering the audio power amplifier, increases gradually from 0 to a predetermined value, a preset circuit, which is used for enabling control circuits of the audio power amplifier, is typically unstable at the beginning and cannot output stable signals to enable the control circuits, such that the control circuits are malfunctioned and the audio power amplifier cannot be operated normally as well.